You really are talking chalk and cheese here.
Small MIG is ok for light fabrication 3mm (1/8"). For 6mm (1/4") or greater you need a larger unit to realistically be effective. Also need a high duty cycle if you want to hardface tractor implements as well as ability to handle .045in wire.
The cheaper option is to buy a smaller MIG for light fabrication. And either a high amp stick welder OR oxyacetylene for heavier applications. Oxyacetylene is great because its portable (power not required, so good for farm gates and field repairs), and also not bad for outdoors with up to a moderate wind.
